Store the Name and Roles service URL in LMSCourse

This will allow us to comunicate with the service outside the launch
context.

See: https://www.imsglobal.org/spec/lti-nrps/v2p0#lti-1-3-integration

lms/models/lms_course.py

@@ -37,6 +37,9 @@ class LMSCourse(CreatedUpdatedMixin, Base):
 
     name: Mapped[str] = mapped_column(index=True)
 
+    lti_context_memberships_url: Mapped[str | None] = mapped_column()
+    """URL for the Names and Roles endpoint, stored during launch to use it outside the launch context."""
+
 
 class LMSCourseApplicationInstance(CreatedUpdatedMixin, Base):
     """Record of on which installs (application instances) we have seen one course."""